1. Field of the Invention

The invention relates generally to double-faced display devices, and more particularly to double-faced field emission display devices.

2. Prior Art

A field emission display device has been widely used in computers, mobile communications and consumer electronics. Conventionally, the field emission display device comprises a fluorescent screen and an electron emission structure. The fluorescent screen comprises an anode plate formed thereat, and the electron emission structure comprises a cathode plate formed thereat. In use, when an emitting voltage is applied between the anode plate and the cathode plate, electrons are emitted from the cathode plate and bombard the fluorescent screen, whereby visible light is produced and an image is displayed on the fluorescent screen. The field emission display device only displays a single image at one surface thereof.

In certain applications, a field emission display device is required to simultaneously display the same image at two opposite surfaces thereof. In order to meet such needs, it is commonplace to simply combine a pair of field emission display devices and thus form a two-sided field emission display device assembly. In the field emission display device assembly, two driving systems are needed. Furthermore, a structure of the field emission display device assembly is complicated. Thus, the field emission display device assembly is bulky and costly.

In order to solve the above-mentioned problems, a so-called double-faced field emission display device has been developed. Referring to FIG. 4, the double-faced field emission display device comprises a pair of parallel fluorescent screens 3, and a cathode plate located between the fluorescent screens 3. Each fluorescent screen 3 acts as an anode plate, and is electrically connected with an anode lead 1. The cathode plate is electrically with a cathode lead 5, and has a plurality of silicon point arrays 2 formed at opposite surfaces thereof. In use, when an emitting voltage is applied between each fluorescent screen 3 and the cathode plate, the silicon point arrays 2 emit electrons. The electrons bombard the fluorescent screen 3, whereby an image is displayed on the fluorescent screen 3.

However, a distance between the cathode plate and each fluorescent screen 3 is in a range from 2 to 30 micrometers. Thus, the emitting voltage needs to be relatively high. In addition, the emission of the electrons cannot be controlled very accurately. Furthermore, a pair of emitting spaces is defined between the cathode plate and the fluorescent screens 3 respectively, with the emitting spaces being independent of each other. This means that when the double-faced field emission display device is manufactured, the emitting spaces must be separately evacuated. Furthermore, the images displayed at the two fluorescent layers 3 may not be identical.

A double-faced field emission display device which overcomes the above-mentioned problems is desired.

Accordingly, an object of the present invention is to provide a double-faced field emission display device having a simple structure, small bulk, and low cost.

To achieve the above-mentioned object, the present invention provides a double-faced field emission display device comprising two parallel fluorescent screens and an electron emission structure located between the fluorescent screens. Each fluorescent screen comprises a transparent substrate with an anode plate and a plurality of coplanar fluorescent layers formed at an inner surface of the transparent substrate. The fluorescence layers comprise three primary colors, such as red, green and blue. The electron emission structure comprises an opaque insulative substrate having two opposite surfaces. Each surface generally faces corresponding fluorescent screen. A plurality of cathode plates and a plurality of insulative layers are alternately formed on each surface of the opaque insulative substrate. Each cathode plate has an electron emitter formed thereon, and each insulative layer has a grid plate formed thereon. The cathode plates and the grid plates are symmetrically interconnected respectively and a single driving system is adopted to achieve simultaneous display same images at the two fluorescent screens.

When the cathode plates are regarded as row electrodes, the grid plates are regarded as column electrodes. Conversely, when the grid plates are regarded as row electrodes, the cathode plates are regarded as column electrodes. Each pair of row electrodes which are symmetrical to the opaque insulative substrate are electrically interconnected. Each pair of column electrodes which are axially symmetrical to a center of the opaque insulative substrate are electrically interconnected. Furthermore, a single driving system is applied in the field emission display device to achieve simultaneous display same images at the two fluorescent screens.

Compared with a conventional double-faced field emission display device, the double-faced field emission display device of the present invention adopts a pair of fluorescent screens and a single driving system to simultaneously display same images at the two fluorescent screens. Furthermore, a plurality of grid plates are adopted, so that the emitting voltage is low and the emission of the electrons can be controlled accurately. The double-faced field emission display device of the present invention has a simple structure, small bulk and low cost, and can be advantageously applied in traffic signal boards, large-scale display boards, surround cinemas and so on.

Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawing, in which:

Referring to FIG. 1, a double-faced field emission display device (not labeled) of the present invention comprises two parallel fluorescent screens 10, 10′, and an electron emission structure 20 located between the fluorescent screens 10, 10′. The fluorescent screen 10 comprises a transparent substrate 11, with an anode plate 12, a plurality of coplanar fluorescent layers 13, and an aluminum film 14 formed at an inner surface (not labeled) of the transparent substrate 10. The anode plate 12 is formed on the inner surface of the transparent substrate 10. The fluorescent layers 13 are coated on the anode plate 12. The aluminum film 14 covers the fluorescent layers 13. The fluorescent layers 13 comprise three primary colors, such as red, green and blue. The fluorescent screen 10′ has substantially the same structure as that of the fluorescent screen 10. The fluorescent screen 10′ comprises a transparent substrate 11′, with an anode plate 12′, a plurality of coplanar fluorescent layers 13′, and an aluminum film 14′ formed at an inner surface (not labeled) of the transparent substrate 10′. The anode plate 12′ is formed on the inner surface of the transparent substrate 10′. The fluorescent layers 13′ are coated on the anode plate 12′. The aluminum film 14′ covers the fluorescent layers 13′. The fluorescent layers 13′ comprise three primary colors, such as red, green and blue.

The electron emission structure 20 comprises an opaque insulative substrate 28 defining a central plane of the structure 20 and having two opposite surfaces 281, 282. The surface 281 generally faces the fluorescent screen 10, and the surface 282 generally faces the fluorescent screen 10′. A plurality of cathode plates 26 and a plurality of insulative layers 24 are alternately formed on the surface 281 of the opaque insulative substrate 28. Each cathode plate 26 has an electron emitter 27 formed thereon, and each insulative layer 24 has a grid plate 25 formed thereon. Each electron emitter 27 generally faces the fluorescent layer 13, and is made of carbon nanotubes, metal or a semiconductive material. In the preferred embodiment, the electron emitters 27 are made of carbon nanotubes. Each carbon nanotube has a small tip. This facilitates point discharging of electrons, and reduces an emitting voltage required for emitting the electrons. Similarly, a plurality of cathode plates 26′ and a plurality of insulative layers 24′ are alternately formed on the surface 281′ of the opaque insulative substrate 28′. Each cathode plate 26′ has an electron emitter 27′ formed thereon, and each insulative layer 24′ has a grid plate 25′ formed thereon. Each electron emitter 27′ generally faces the fluorescent layer 13′, and is made of carbon nanotubes, metal or a semiconductive material. In the preferred embodiment, the electron emitters 27′ are made of carbon nanotubes.

The fluorescent screen 10 and the electron emission structure 20 define an emitting space 31 therebetween, and the fluorescent screen 10′ and the electron emission structure 20 define an emitting space 31′ therebetween. Four side walls 30 surround and enclose the emitting space 31, and four side walls 30′ surround and enclose the emitting space 31′. With the opaque insulative substrate 28, the emitting space 31 and the emitting space 31′ are independent of each other. Furthermore, four through holes 29 are defined in four corners of the opaque insulative substrate 28. Thus, the emitting space 31 and the emitting space 31′ can be evacuated simultaneously.

For the fluorescent screen 10, there are two kinds of electrode configurations possible. The first configuration is: the cathode plates 26 are regarded as row electrodes, and the grid plates 25 are regarded as column electrodes. The second configuration is: the grid plates 25 are regarded as row electrodes, and the cathode plates 26 are regarded as column electrodes. The interconnections of the electrodes 25, 26 in the two configurations are similar. In the preferred embodiment, the first configuration is adopted. Similarly, for the fluorescent screen 10′, a configuration analogous to the first configuration is adopted for the grid plates 25′ and the cathode plates 26′.

FIG. 2 is a schematic diagram showing connections of row cathode plates 26, 26′. The cathode plates 26, 26′ at a first row which are symmetrical to the opaque insulative substrate 28 are labeled as 261, 261′, and the cathode plates 26, 26′ at a second row which are symmetrical to the opaque insulative substrate 28 are labeled as 262, 262′. The cathode plates 261, 261′ are electrically interconnected, and the cathode plates 262, 262′ are electrically interconnected. Similarly, other cathode plates 26, 26′ at same rows which are symmetrical to the opaque insulative substrate 28 are electrically interconnected. FIG. 3 is a schematic diagram showing connections of column grid plates 25, 25′. A first pair of column grid plates 25, 25′ which are axially symmetrical to a center of the opaque insulative substrate 28 are labeled as 251, 251′, and a second pair of column grid plates 25, 25′ which are axially symmetrical to the center of the opaque insulative substrate 28 are labeled as 252, 252′. The grid plates 251, 251′ are electrically interconnected, and the grid plates 252, 252′ are electrically interconnected. Similarly, other pairs of column grid plates 25, 25′ which are axially symmetrical to the center of the opaque insulative substrate 28 are electrically interconnected.

A single driving system 40 is applied in the double-faced field emission display device. When an emitting voltage is applied between the grid plates 25 and the cathode plates 26, the electron emitters 27 emit electrons. The electrons bombard the fluorescent layer 13, the fluorescent layer 13 luminesces in accordance with the three primary colors, and visible light is emitted from an outer surface of the transparent substrate 11. Thereby, a first image is displayed on the fluorescent screen 10.

Similarly, the electron emitters 27′ emit electrons. The electrons bombard the fluorescent layer 13′, the fluorescent layer 13′ luminesces in accordance with the three primary colors, and visible light is emitted from an outer surface of the transparent substrate 11′. Thereby, a second image the same as the first image is displayed on the fluorescent screen 10′.

Compared with a conventional double-faced field emission display device, the double-faced field emission display device of the present invention adopts a pair of fluorescent screens 10, 10′ and a single driving system to simultaneously display same images at the two fluorescent screens 10, 10′. Furthermore, a plurality of grid plates 25, 25′ are adopted, so that the emitting voltage is low and the emission of the electrons can be controlled accurately. The double-faced field emission display device of the present invention has a simple structure, small bulk and low cost, and can be advantageously applied in traffic signal boards, large-scale display boards, surround cinemas, and so on.

It is to be understood that the above-described apparatus is intended to illustrate rather than limit the invention. Variations may be made to the apparatus without departing from the spirit of the invention. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.